1. Field of the Invention
The present invention relates to a zoom lens of a small size and widely variable magnification.
2. Discussion of the Background
Zoom lenses having a field angle ranging from 62.degree. to 19.degree. are disclosed in Japanese Laid-Open patent Publications Nos. 56-133713, 57-164709, 59-160121, 60-14212, 61-62012, and 61-69016, for example. The disclosed zoom lenses are not compact since the ratio (L/f.sub.T) of the overall length L of the lens system (from the front lens surface to the image plane at the wide angle end) to the focal length f.sub.T at the telephoto end is greater than 1.
The most general way of focusing a zoom lens is to move the first lens group of the zoom lens. This method is advantageous in that the amount of movement of the first lens group remains unchanged at all focal length settings. However, if a zoom lens has a wide angle setting and the first lens group has positive refracting power, then the vignetting becomes greater unless the diameter of the front lens element is increased. If the diameter of the front lens element is increased, then the zoom lens becomes heavier, larger, and more costly.
One solutionn to the above problems is to move, in unison, a first lens group having positive refracting power and a second lens group having negative refracting power. Since the combined power of the first and second lens groups is large in the wide angle end, the amount of movement of the first and second lens groups is small, and the front lens element can be reduced in diameter. However, close ranges in a zooming range are limited in view of the amount of movement in unison of the first and lens groups, the diameter of the front lens element, and the performance thereof.